Messier Objects

Hydra, also called the serpent of Lerna, was a beast with the body of
a hound and 100 serpentine heads. As if this weren't bad enough, it
also had poisonous breath and it was so hideous that it caused most
people to die of fear from simply seeing it. One of Hercules' great tasks was to kill this
monster. When he started to fight it, he discovered that every time
he cut off one of the heads, three grew back in place of it. Seeing
this was getting him nowhere, he had his charioteer, Iolus, burn the
stump after each time he cut off a head, which prevented the
unfortunate regeneration. The last head was immortal, however, so
after cutting it off, they trapped it under a rock.

Hydra is a very weird constellation. It is the largest constellation
on the sky (with Virgo close behind), but is strung out from Libra to Canis
Minor along the southern horizon over about 90 degrees. Believe it
or not, it used to be even bigger, but like the old Argo Navis constellation, it was split into
four parts. Various stellar cartographers, including Flamsteed and
Hevelius, broke the old Hydra into Sextans
(the sextant), Crater (the cup), Corvus (the crow) and a new, reduced Hydra.

Felis, the Cat
In addition to these three new constellations, an obscure French
astronomer added a constellation of his own to a star chart he
created. In between Hydra, Antlia and Pyxis, he drew a little cat and named it Felis.
However, Felis was not officially adopted, so it remains merely an
anecdote...